Glass molding system and related apparatus and method

ABSTRACT

A glass molding system and a method of making glass articles using the glass molding system are disclosed. The glass molding system includes an indexing table, a plurality of enclosures arranged along the indexing table, and a plurality of stations defined on the indexing table such that each of the stations is selectively indexable with any one of the enclosures. At least one radiant heater is arranged in at least one of the enclosures. A radiation reflector surface and a radiation emitter body are arranged in the at least one of the enclosures. The radiation emitter body is between the at least one radiant heater and the radiation reflector surface and has a first surface in opposing relation to the at least one radiant heater and a second surface in opposing relation to the radiation reflector surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims the benefit of priorityunder 35 U.S.C. §120 of U.S. patent application Ser. No. 13/480,172,filed on May 24, 2012, and which claims the benefit of priority under 35U.S.C. §119 of U.S. Provisional Application Ser. No. 61/490,923 filed onMay 27, 2011. Both these applications are incorporated by referenceherein in their entirety.

TECHNICAL FIELD

The present invention relates generally to manufacture ofthree-dimensional (3D) glass articles by thermal reforming oftwo-dimensional (2D) glass sheets.

BACKGROUND

There is a large demand for 3D glass covers for portable electronicdevices such as laptops, tablets, and smart phones. A particularlydesirable 3D glass cover has a combination of a 2D surface, forinteraction with a display of an electronic device, and a 3D surface,for wrapping around the edge of the display. The 3D surface may be anundevelopable surface, i.e., a surface that cannot be unfolded orunrolled onto a plane without distortion, and may include anycombination of bends, corners, and curves. The bends may be tight andsteep. The curves may be irregular. Such 3D glass covers are complex anddifficult to make with precision using machining processes such asgrinding and milling. Thermal reforming has been used to successfullyform 3D glass articles from 2D glass sheets in other types ofapplications.

The present invention relates to a system that enables use of thermalreforming to make 3D glass covers such as described above. The presentinvention also relates to a process of forming a plurality of 3D glassarticles with consistent shapes and high dimensional accuracy.

SUMMARY

In one aspect of the present invention, a glass molding system includesan indexing table, a plurality of enclosures arranged along the indexingtable, and a plurality of stations defined on the indexing table suchthat each of the stations is selectively indexable with any one of theenclosures. At least one radiant heater is arranged in at least one ofthe enclosures. A radiation reflector surface is arranged in the atleast one of the enclosures in opposing relation to the at least oneradiant heater. A radiation emitter body is arranged in the at least oneof the enclosures between the at least one radiant heater and theradiation reflector surface. The radiation emitter body has a firstsurface in opposing relation to the at least one radiant heater and asecond surface in opposing relation to the radiation reflector surface.

In one embodiment, the glass molding system further includes a coolingapparatus disposed at least partially in the at least one of theenclosures and operable to remove heat from the radiation emitter body.

In one embodiment, the glass molding system further includes a pluralityof molds and mold supports, each mold support configured to support oneof the molds at one of the stations.

In one embodiment, the radiation reflector surface has an opening forreceiving any one of the molds such that the radiation reflector surfacecircumscribes the mold.

In one embodiment, the area of the opening in the radiation reflectorsurface is less than an area of the second surface of the radiationemitter body.

In one embodiment, the glass molding system further includes a coolingplate for cooling any one of the molds. The cooling plate is configuredto be mounted below the mold in a spaced-apart relation when the mold issupported at one of the stations by one of the mold supports.

In one embodiment, the cooling plate comprises a plate member having afirst flow channel in which the cooling plate receives fluid, a secondflow channel from which the cooling plate discharges fluid, and abarrier between the first flow channel and second flow channel thatallows fluid to cross over from the first flow channel to the secondflow channel at several points along an entire length of the second flowchannel.

In one embodiment, the glass molding system further includes a heatingapparatus arranged along the indexing table for preheating any one ofthe molds while the mold is at a station that is not indexed with anyone of the enclosures. The configuration of the heating apparatus andarrangement of the heating apparatus relative to the indexing table issuch that any of the stations can be indexed with the heating apparatus.

In one embodiment, the heating apparatus includes at least one radiantheater.

In one embodiment, the heating apparatus is configured to boost thetemperature of any one of the molds by a predetermined amount in asingle dwell of the indexing table.

In one embodiment, the glass molding system further comprises means formeasuring a shape of a 3D glass article produced by any one of themolds.

In one embodiment, the measuring means comprises a measuring surface,support elements on the measuring surface for supporting the 3D glassarticle in a plane substantially parallel to the measuring surface, andat least one displacement gauge configured to measure a displacement ofa point on the 3D glass article when the 3D glass article is supportedby the support elements.

In one embodiment, the measuring means further includes means foraligning the 3D glass article on the measuring surface.

In one embodiment, the measuring means further comprises means forclamping the 3D glass article to the support elements.

In one embodiment, the glass molding system further includes means forloading 2D glass sheets onto the molds and means for unloading 3D glassarticles from the molds.

In one embodiment, the glass molding system further comprises means forpreheating the 2D glass sheets outside of the enclosures.

In one embodiment, each of the enclosures is a thermal enclosureprovided by a housing having an insulated refractory wall.

In one embodiment, the at least one radiant heater is an infraredradiant heater.

In one embodiment, the radiation emitter body emissivity is greater than0.8 and the radiation reflector surface emissivity is less than 0.4.

In one embodiment, the second surface of the radiation emitter body andthe radiation reflector surface are spaced apart by a gap in a rangefrom 10 mm to 50 mm.

In one embodiment, the radiation reflector surface is formed on theindexing table, and the indexing table is movable through the enclosuresto position the radiation reflector surface in the at least one of theenclosures.

In one embodiment, the indexing table is a rotary indexing table.

In another aspect of the present invention, a method of making glassarticles includes placing a 2D glass sheet on a mold having a moldsurface with a 3D shape. The 2D glass sheet and mold are placed in aradiative environment, and the 2D glass sheet is heated to a firsttemperature between an annealing point and a softening point of theglass. While in the radiative environment, the 2D glass sheet isconformed to the mold surface by force to form a 3D glass article. The3D glass article is held against the mold surface by force whilebringing the temperature of the 3D glass article and mold to a secondtemperature. The force holding the 3D glass article against the mold isreleased. Then, the 3D glass article is rapidly cooled to a thirdtemperature below a strain point of the glass.

In one embodiment, the force used in conforming the 2D glass sheet tothe mold surface is greater than the force used in holding the 3D glassarticle against the mold surface.

In one embodiment, vacuum is applied between the mold surface and the 2Dglass sheet or 3D glass article to generate each of the conforming andholding forces.

In one embodiment, the method further includes adjusting at least oneprocess parameter to control the shape of the 3D glass article.

In one embodiment, adjusting at least one process parameter includesadjusting a temperature of the mold while releasing the force holdingthe 3D glass article against the mold.

In one embodiment, adjusting the temperature of the mold includescooling of the mold. In one embodiment, the cooling is by radiative heattransfer.

In one embodiment, adjusting the temperature of the mold furtherincludes determining a set of shape metrics that defines thecharacteristics of the shape of the 3D glass article.

In one embodiment, adjusting the temperature of the mold furtherincludes determining an amount of heat to remove from the mold based onan accuracy of at least one shape metric of a 3D glass article producedpreviously by the mold.

In one embodiment, the cooling includes circulating a cooling fluidthrough a cooling plate, and determining the amount of heat to removeincludes determining a flow rate at which the cooling fluid is suppliedto the cooling plate.

In one embodiment, heating the 2D glass sheet in the radiativeenvironment comprises using a radiation emitter body to emit radiationthat is absorbed by the 2D glass sheet.

In one embodiment, the radiation emitter body absorbs radiation from atleast one infrared radiant heater during heating of the 2D glass sheetin the radiative environment.

In one embodiment, bringing the 3D glass article and mold to the secondtemperature includes using a radiation emitter body to absorb heat fromthe 3D glass article.

In one embodiment, the method further includes removing heat from theradiation emitter body while the radiation emitter body is absorbingheat from the 3D glass article.

In one embodiment, the method further includes selectively deliveringheat to the radiation emitter body to maintain the radiation emitterbody at the second temperature while the radiation emitter body isabsorbing heat from the 3D glass article.

In one embodiment, the method further includes separately preheating the2D glass sheet and mold prior to placing the 2D glass sheet on the mold.

In another aspect of the present invention, a heat exchanger apparatusincludes a main body, which includes a first flow channel and a secondflow channel separated by a convoluted encircling wall. The convolutedencircling wall is configured such that fluid can pass from the firstflow channel into the second flow channel over the convoluted wall. Themain body further includes at least two flow channel ports, a first flowchannel port through which fluid can be supplied into the first flowchannel and a second flow channel port through which fluid can bedischarged from the second flow channel. The main body further includesa flow distribution channel separate from the first and second flowchannels. The flow distribution channel is in communication with thefirst flow channel and configured to distribute fluid to a plurality ofpoints along a length of the first flow channel.

In one embodiment, the main body is in the form of a plate, and the heatexchanger apparatus further includes a front cover plate member coveringa front side of the main body where the first flow channel, the secondflow channel, and the convoluted wall are located. The covering providedby the front cover plate is such that a gap is formed between the frontcover plate member and the main body where the convoluted wall islocated.

In one embodiment, the heat exchanger apparatus further includes aplurality of spacers arranged between the main body and the front coverplate member to maintain the gap at a uniform height along theconvoluted wall.

In one embodiment, the front cover plate member sealingly engages themain body to allow pressurizing of fluid in the first flow channel inorder to enable the fluid in the first flow channel to pass into thesecond flow channel over the convoluted wall.

In one embodiment, the heat exchanger apparatus further comprises a backcover plate member covering a back side of the main body where the flowdistribution channel is located. The back cover plate member has atleast two flow ports, a first flow port for supplying fluid to the mainbody and a second flow port for withdrawing from the main body. Thecovering provided by the back cover plate member is such that the firstflow port is in communication with the flow distribution channel and thesecond flow port is in communication with the second flow channel port.

In another aspect of the present invention, an apparatus for measuring ashape of an article includes a measuring surface and a plurality ofsupports arranged on the measuring surface for stably supporting thearticle. The apparatus further includes at least one alignment guideadjacent to the measuring surface and serving as a reference datum forplacing the article relative to the measuring surface. The apparatusfurther includes at least one displacement gauge for measuring adisplacement of a point on the article when the article is arranged onthe supports.

In one embodiment, the at least one displacement gauge includes anon-contact displacement sensor.

In one embodiment, the non-contact displacement sensor is selected froma group consisting of a laser triangulation sensor, a spectralinterference laser displacement sensor, and a confocal chromaticdisplacement sensor.

In one embodiment, the shape measuring apparatus further includes meansfor clamping the article to the supports.

In one embodiment, the clamping means includes axial holes in thesupports through which vacuum can be applied to the article when thearticle is on the supports.

In one embodiment, the measurement surface is provided by a mountingblock having at least one opening in which the at least one displacementgauge is arranged.

In one embodiment, the shape measuring apparatus includes means forclamping the at least one displacement gauge to the mounting block.

In another aspect of the present invention, an apparatus for measuring ashape of an article includes a first fixture for supporting the article,a second fixture arranged in opposing relation to the first fixture, anda plurality of displacement gauges supported along the second fixture inpositions to measure displacements of a plurality of points on thearticle when the article is supported on the first fixture.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary of the presentinvention and are intended to provide a framework for understanding thenature and character of the present invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe present invention and are incorporated in and constitute a part ofthis specification. The drawings illustrate various embodiments of theinvention and together with the description serve to explain theprinciples and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a description of the figures in the accompanyingdrawings. The figures are not necessarily to scale, and certain featuresand certain views of the figures may be shown exaggerated in scale or inschematic in the interest of clarity and conciseness.

FIG. 1 is a perspective view of a glass molding system.

FIG. 2 is a cross-section of a heat transfer module.

FIG. 3 is a cross-section of a heat transfer module incorporating anapparatus for cooling a radiative emitter body.

FIG. 4A is a side view of a cooling plate.

FIG. 4B is a top view of a middle plate of the cooling plate of FIG. 4A.

FIG. 4C is a cross-sectional view of the cooling plate of FIG. 4B alongline 4C-4C.

FIG. 4D is a bottom view of the middle plate of FIG. 4B.

FIG. 4E is a top view of a bottom plate of the cooling plate of FIG. 4A.

FIG. 5A is a cross-sectional view of a mold support system.

FIG. 5B is a perspective view of a subassembly of the mold supportsystem of FIG. 5A.

FIG. 6A is a perspective view of a metrology system.

FIG. 6B is a cross-section of the metrology system shown in FIG. 6A.

FIG. 6C is a perspective view of another metrology system.

FIG. 6D is a graph showing repeatability of measurements made by themetrology system of FIG. 6C.

FIG. 6E is a partial cross-section of another metrology system.

FIG. 7A is a perspective view of a preheating module.

FIG. 7B is a section of a glass molding system with the preheatingmodule of FIG. 7A.

FIG. 7C is a cross section of FIG. 7B along line 7C-7C.

FIG. 8 is a graph showing the effect of changing cooling plate flow onthe shape of a 3D glass article, as measured by the metrology system ofFIGS. 6A and 6B.

FIG. 9A is a block diagram of a system for controlling glass shape.

FIG. 9B is a block diagram of another system for controlling glassshape.

FIG. 10A is a schematic of a shape defining metric.

FIG. 10B is another schematic of shape defining metrics.

FIG. 11A is a graph showing influence of air flow rate on moldtemperature.

FIG. 11B is another graph showing influence of air flow rate on moldtemperature

FIG. 12 is a graph illustrating a process of making a 3D glass article.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details may beset forth in order to provide a thorough understanding of embodiments ofthe invention. However, it will be clear to one skilled in the art whenembodiments of the invention may be practiced without some or all ofthese specific details. In other instances, well-known features orprocesses may not be described in detail so as not to unnecessarilyobscure the invention. In addition, like or identical reference numeralsmay be used to identify common or similar elements.

FIG. 1 shows a glass molding system 100 for producing 3D glass articlesfrom 2D glass sheets by thermal reforming. The glass molding system 100includes a primary rotary table system 102 having a primary rotaryindexing table 104. The primary rotary table system 102 can be anycustom or commercial rotary table system capable of translating theprimary rotary indexing table 104 along a circular or looped paththrough a selected rotational angle. In alternate embodiments, anon-rotary table system, such as a linear table system, with anon-rotary indexing table, such as a linear indexing table, may be usedin lieu of a rotary table system with a rotary indexing table. Severalstations 106 are defined on the primary rotary indexing table 104, andeach station 106 includes a support for a mold 108. Heat transfer (HT)modules 110 are arranged along the primary rotary indexing table 104,and the primary rotary indexing table 104 can be rotated to allow eachstation 106 to be selectively indexed with any one of the HT modules110. When a station 106 is indexed with a HT module 110, a mold 108supported at the station 106 is disposed within the HT module 110,allowing a 2D glass sheet supported on the mold 108 to undergo at leasta portion of a thermal reforming process within the HT module 110.Typically, the number of stations 106 will exceed the number of HTmodules 110 so that only some of the stations 106 are indexed with HTmodules 110 at any time. In the embodiment shown in FIG. 1, there aretwenty-four stations 106 and eighteen HT modules 110, but there isplenty of leeway in selecting the number of stations 106 and HT modules110 in the system. Each station 106 that is not indexed with a HT module110 is typically open to the air to allow operations such as loading ofa 2D glass sheet into a mold, unloading of a 3D glass article from amold, cleaning of a mold, and repairing or replacement of a mold to becarried out.

Each cycle of the glass molding system 100 includes an indexing periodfollowed by a wait period. During the indexing period, the primaryrotary indexing table 104 is rotated by a selected rotational angle in aselected direction (which may be clockwise or counterclockwise), whichresults in a particular configuration of stations 106 being indexed withthe HT modules 110. The rotational speed may be constant or variedduring the indexing period. One example of a variation is an initialacceleration, followed by a steady speed, followed by a finaldeceleration. For the first cycle, it may be that only one of thestations 106 indexed with the HT modules 110 supports a mold 108carrying a 2D glass sheet. After a few more cycles, all the stations 106indexed with the HT modules 110 would each support a mold 108 carrying a2D glass sheet or a mold 108 carrying a 3D glass article or an emptymold 108. Whether the mold 108 is carrying a 2D glass sheet or a 3Dglass article or is empty would depend on the position of the mold 108along the sequence of HT modules 110. During the wait period, thermalreforming of a 2D glass sheet into a 3D glass article is carried out ateach station 106 that is indexed with a HT module 110. For continuousproduction, it may not be feasible to complete thermal reforming in asingle HT module 110, in which case thermal reforming may be distributedamong a series of HT modules 110.

A typical thermal reforming process involves heating the 2D glass sheetto a forming temperature, e.g., a temperature in a temperature rangecorresponding to a glass viscosity of 10⁷ Poise to 10¹¹ Poise or betweenan annealing point and softening point of the glass, while the 2D glasssheet is on top of a mold. The heated 2D glass sheet may start saggingonce heated. Typically, vacuum is then applied in between the glasssheet and mold to conform the glass sheet to the mold surface andthereby form the glass into a 3D glass article. After forming the 3Dglass article, the 3D glass article is cooled to a temperature below thestrain point of the glass, which would allow handling of the 3D glassarticle. For distributed thermal reforming, a segment of the HT modules110 could be devoted to heating the 2D glass sheet to a formingtemperature, another segment of the HT modules 110 could be devoted toforming the 2D glass sheet into the 3D glass article, and anothersegment of the HT modules 110 could be devoted to cooling the 3D glassarticle to a temperature below the strain point of the glass.

The cycle described above is repeated as many times as desired forcontinuous production of 3D glass articles from 2D glass sheets bythermal reforming. While the cycles are ongoing, additional activitiesare taking place such as unloading 3D glass articles from molds andloading new 2D glass sheets into empty molds. As the primary rotaryindexing table 104 is rotated, each of the stations 106 supporting amold 108 carrying a 3D glass article will eventually become exposed tothe air, allowing access to the 3D glass article. A robot 112 may thenbe used to unload the 3D glass article from the mold 108 onto anunloading area 114. Also, a robot 116 may be used to load new 2D glasssheets from a loading area 118 onto the emptied mold 108. To enable ahigh throughput, the 2D glass sheets are preheated before being loadedonto the mold 108. For this purpose, the loading area 118 includes asecondary rotary indexing system 120, which includes a secondary rotarytable 122. Several stations are defined on the secondary rotary indexingtable 122, as in the case of the primary rotary indexing table 104. Thesecondary rotary indexing table 122 is disposed in a furnace 124. 2Dglass sheets are first loaded onto the stations of the secondary rotaryindexing table 122 and preheated in the furnace 124. In one embodiment,preheating of the 2D glass sheets includes flowing heated gas, such asnitrogen, over the 2D glass sheets. The 2D glass sheets are heated to atemperature below the forming temperature. The robot 116 then transfersthe preheated 2D glass sheets onto the stations 106 of the primaryrotary indexing table 104 for further heating and forming into 3D glassarticles by thermal reforming. In one example, the secondary rotaryindexing table 122 has six stations, but there is no particularrestriction on how many stations may be defined on the secondary rotaryindexing table 122. The robots 116, 112 may use vacuum or suction cupsto grab the 2D glass sheets and 3D glass articles, respectively. Thevacuum or suction cups or other means of grabbing the 2D glass sheetsand 3D glass articles preferably should not scratch the glass, mar theglass, or leave residue on the glass.

The HT modules 110 do not need to be identical. Some of the HT modules110 may be configured for active heating. Some of the HT modules 110 maybe configured for active cooling. Some of the HT modules 110 may beconfigured to neither actively cool nor heat and may simply provide astable thermal environment, e.g., via insulation, where a desiredtemperature may be maintained or allowed to drop slowly. Specificexamples of HT modules that could be used as the HT modules 110 will bedescribed below. In these specific examples, radiant heaters arepreferably used for heating. However, other means of heating may be alsoused.

FIG. 2 shows a HT module 200 that could be used as any one of the HTmodules 110 described above. The heating module 200 includes a housing202, which defines a thermal enclosure 204. A thermal enclosure is anenclosure that can maintain its contents at a temperature other thanambient. The wall of the housing 202 has a wall layer 203 made of arefractory material and surrounding the thermal enclosure 204, a walllayer 205 made of a refractory material and surrounding portions of thewall layer 203, and a wall layer 207 made of insulating material andsurrounding the wall layers 203, 205. The insulated refractory wall ofthe housing 202 allows the temperature in the thermal enclosure 204 tobe controllable. An array of heaters 206 is disposed in the upperportion 209 of the thermal enclosure 204. Preferably, the heaters 206are radiant heaters. A radiant heater heats by radiant energy. Examplesof radiant energy sources are microwaves, radio waves, visible light,infrared heat, and electricity. Preferably, the radiant heaters areinfrared radiant heaters. The heaters 206 may also be resistive heatersin other embodiments. A radiation emitter body 208 is also disposed inthe upper portion 209 of the thermal enclosure 204, below the array ofheaters 206. The radiation emitter body 208 is a physical body that canemit or absorb radiation. In one embodiment, the radiation emitter body208 is secured to the housing 202, for example, by inserting the ends ofthe radiation emitter body 208 into grooves 211 in the refractory layer203 of the housing 202.

A radiation reflector surface 210 is disposed in the thermal enclosure204, below the radiation emitter body 208. In one embodiment, theradiation reflector surface 210 is an integral part of the HT module200, e.g., the radiation reflector surface 210 may be supported on asurface in the thermal enclosure 204 or secured to the wall of thehousing 202. In this embodiment, the radiation reflector surface 210would be stationary. In another embodiment, such as shown in FIG. 2, theradiation reflector surface 210 is provided by or formed on a surface ofthe indexing table 104. In this embodiment, the radiation reflectorsurface 210 would be capable of moving through the thermal enclosure 204with the indexing table 104. The radiation reflector surface 210 has areceiving area, which is a designated area for receiving a mold, e.g.,mold 214. In one embodiment, the receiving area of the radiationreflector surface 210 includes a receiving hole 212 sized to receive amold, e.g., mold 214.

The lower portion 213 of the thermal enclosure 204 includes an opening215 for running the indexing table 104 through the thermal enclosure204. In FIG. 2, a station on the indexing table 104 has been indexedwith the HT module 200 so that a mold 214 at the station is placed inthe thermal enclosure 204. The mold 214 is also placed in the receivinghole 212 of the radiation reflector surface 210 that is arranged in thethermal enclosure 204. The placement of the mold 214 in the receivinghole 212 allows the radiation reflector surface 210 to surround aperiphery of the mold 214. With this placement, the top of the mold 214may or may not be flush with the radiation reflector surface 210.

The array of radiant heaters 206 emits radiation, which is received atthe top surface 222 of the radiation emitter body 208 and absorbed intothe radiation emitter body 208. Radiation is absorbed or emitted at thebottom surface 216 of the radiation emitter body 208, depending on thetemperature of objects below the bottom surface 216. The operatingtemperature of the radiation emitter body 208 dictates the spectralenergy that impinges on objects below the bottom surface 216. The arrayof radiant heaters 206 in combination with the radiation emitter body208 provides a thermally-uniform heat source for mold 214 and glasscarried by the mold 214. The radiation not absorbed by the mold 214 andglass is reflected back to the radiation emitter body 208 by theradiation reflector surface 210.

In one embodiment, the radiation reflector surface 210 is a flatsurface. In one embodiment, the bottom surface 216 of the radiationemitter body 208 is flat and opposed to the radiation reflector surface210. In one embodiment, the radiation reflector surface 210 and thebottom surface 216 of the radiation emitter body 208 are substantiallyparallel to each other. The radiation reflector surface 210 may be asurface of a plate or may be plating on any suitable surface, such as asurface of the indexing table 104. In one embodiment, the radiationreflector surface 210 is made of a refractory material, e.g.,alumina-containing ceramic material available from ZIRCAR RefractoryComposites, Inc. In one embodiment, the radiation reflector surface 210has a relatively low emissivity, preferably an emissivity less than 0.4.In one embodiment, the radiation emitter body 208 is a plate. In oneembodiment, the radiation emitter body 208 has a relatively highemissivity, preferably an emissivity greater than 0.8. Preferably, theemissivity of the radiation emitter body 208 is higher than that of theradiation reflector surface 210. An example of a suitable material forthe radiation emitter body 208 is silicon carbide. The materials of theradiation emitter body 208 and the radiation reflector surface 210should be appropriate for the high temperatures that would beencountered within the thermal enclosure 204, i.e., temperatures atwhich glass can be reformed.

To achieve an infinite parallel plate heat system, along with selectingthe emissivity of the radiation reflector surface 210 to be low, e.g.,less than 0.4, the area of the bottom surface 216 of the radiationemitter body 208 is selected to be much larger than the area of thereceiving hole 212 in the radiation reflector surface 210 (or the areaof the top of the mold 214). In one embodiment, the area of the bottomsurface 216 of the radiation emitter body 208 is approximately 9 timeslarger than the area of the receiving hole 212 of the radiationreflector surface 210 (or the area of the top of the mold 214). The spanof the bottom surface 216 of the radiation emitter body 208 may begreater than or approximately the same as the span of the radiationreflector surface 210. The radiation view factor of the system ispreferably selected to maximize the efficiency of heat transfer of thesystem. This may be achieved in one embodiment by locating the top ofthe mold 214 (or the radiation reflector surface 210 which includes thereceiving hole 212 for the mold 214) close to the bottom surface 216 ofthe radiation emitter body 208, preferably 10 mm to 50 mm from thebottom surface 216 of the radiation emitter body 208.

Additional radiant heaters 218 may be arranged between the plurality ofradiant heaters 206 and the radiation emitter body 208 to provideadditional heat to the radiation emitter body 208 where needed. Forexample, additional heat may be needed in portions of the radiationemitter body 208 near the periphery of the thermal enclosure 204. Theadditional radiant heaters 218 and the plurality of radiant heaters 206are controlled to uniformly heat the radiation emitter body 208 so thatthe radiation emitter body 208 uniformly heats the glass and mold 214.The temperature of the radiation emitter body 208 or of the spacebetween the heaters 206, 218 and the radiation emitter body 208 can bemonitored using suitable temperature sensors, and the output of thesensors can be used to control the output of the heaters 206, 218.

The ends of the radiant heaters 206, 218 protrude through the wall ofthe housing 202 and are encased in perforated end plates 220 mounted onthe exterior of the housing 202. These ends include electricalconnectors for connection of the radiant heaters 206, 218 to anelectrical source. To protect these electrical connectors, theperforations in the end plates 220 can be used to circulate cooling airaround the electrical connectors.

A mold assembly 226 is shown at the opening 215. The mold assembly 226extends into the opening 215 through a station of the indexing table104. The mold assembly 226 includes the mold 214 mentioned above and asupport 228 for the mold 214. The mold support 228 may incorporate atilting stage for tilting the mold 214 while the mold 214 is received inthe receiving hole 212 (or receiving area) of the radiation reflectorsurface 210 (the relevance of the tilting capability is that one methodof aligning glass on the mold 214 requires that the mold 214 is tilted).A suitable positioning system attaches the mold support 228 to theindexing table 104 so that the mold assembly 226 can travel with theindexing table 104. The mold assembly 226 may further include a conduit(or conduits) for applying vacuum to the mold 214 and a conduit (orconduits) for applying gas around the mold 214. The gas applied aroundthe mold 214 may be for cooling the 3D glass article on the mold afterthe 3D glass article has been formed. The details of the mold 214 arenot disclosed here. Typically, the mold 214 would have a mold surfacehaving a 3D profile that corresponds to the 3D shape of the glassarticle to be formed using the mold. The mold 214 would also have portsthrough which vacuum can be applied to the glass to draw the glassagainst the mold surface. The ports would open to the mold surface andbe in communication with the conduit(s) for applying vacuum to the mold214.

The HT module 200 may operate in a heating mode, where the radiationemitter body 208 is emitting radiation, or a cooling mode, where theradiation emitter body 208 is absorbing radiation. For a HT module 200operating in a heating mode, the glass indexed into the heating HTmodule 200 will absorb radiation emitted by the radiation emitter body208. This absorption will continue until one of two events occurs: (i)the temperature of the glass is about the same as that of the radiationemitter body 208 or (ii) the glass is indexed out of the HT module 200.For a HT module 200 operating in a cooling mode, the glass indexed intothe cooling HT module 200 will emit radiation, which will be absorbed bythe radiation emitter body 208. This emission will continue until one oftwo events occurs: (i) the temperature of the glass is about the same asthat of the radiation emitter body 208 or (ii) the glass is indexed outof the cooling HT module 200.

FIG. 3 shows a HT module 300 that is essentially the HT module 200 (inFIG. 2) plus a cooling apparatus 302. That is, if the cooling apparatus302 is not used, the HT module 300 will operate in the same manner asdescribed above for HT module 200. The HT module 300 is more efficientfor cooling glass than the HT module 200, as will be explained below. Inexplaining the configuration of the HT module 300, parts of the HTmodule 200 already described above will be reused.

The cooling apparatus 302 includes a cooling plate 304, which isarranged inside the thermal enclosure 306 of the HT module 300. Thecooling plate 304 is between the radiant heaters 206 and the upper wall310 of the HT module 300. The arrangement of the cooling plate 304 issuch that there is a radiation view of the cooling plate 304 from theradiation emitter body 208. The cooling plate 304 has an internalchamber 314. A plenum 316 is formed above the cooling plate 304 fordistributing fluid into the internal chamber 314 of the cooling plate304. Pores 318 are provided in the portion of the cooling plate 304adjacent to the plenum 316 for fluid communication between the plenum316 and the internal chamber 314.

A fluid supply tube 320 extends through the roof 310 of the HT module300 to the plenum 316 and is used to supply cooling fluid to the plenum316. The cooling fluid in the plenum 316 is forced through the pores 318of the cooling plate 304 into the internal chamber 314 of the coolingplate 304. The cooling fluid impinges on the inside wall of the coolingplate 304 in the form of jets. The impinging jets have the advantage ofproviding a large heat transfer over a small area. The cooling fluid istypically air, and the flow rate is typically less than 200 liters perminute. Two fluid discharge tubes 322, 324 extend through the roof 310of the HT module 300 to the cooling plate 304 and are used to removefluid from the internal chamber 314 of the cooling plate 304. The riskof particle contamination inside the thermal enclosure 306 from thecooling apparatus 302 is low because the cooling fluid is completelycontained within the cooling apparatus 302. Preferably, the coolingfluid is a gas, such as air, so that if there is any leakage from thecooling apparatus 302 the leakage would not interfere with operation ofthe radiant heaters 206. The cooling fluid being completely containedwithin the cooling apparatus 302 also has the advantage of lowering thethermal gradients across the fluid tubes 320, 322, 324 so that thetemperature across the cooling plate 304 is somewhat uniform.

For cooling of the glass, the radiant emitter body 208 has to be set atsome temperature that will determine the temperature to which the glasson the mold 214 is to be cooled. As the radiation emitter body 208absorbs radiation from the glass and mold 214 and radiation reflectorsurface 210, the temperature of the radiant emitter body 208 willincrease. The purpose of the cooling apparatus 302 is to remove thisexcess heat from the radiation emitter body 208 so that the radiationemitter body 208 is at the desired set temperature. Without thiscooling, the glass will end up at a higher temperature than desired.Achieving the proper temperature is one aspect of the cooling. Anotheraspect is to cool the glass in a controlled manner to avoidthermally-induced stresses that may later result in defects such aswarpage in the glass. Controlled cooling of the glass is achieved inpart by using the radiant heaters 206 to selectively deliver heat to theradiation emitter body 208 while using the cooling apparatus 302 toremove heat from the radiation emitter body 208. The amount of heatdelivered to the radiation emitter body 208 is based on the temperatureof the radiation emitter body 208 as it absorbs radiation and is beingcooled by the cooling apparatus 302. The temperature of the radiationemitter body 208 may be monitored directly via measuring withtemperature sensors or indirectly via measuring output of the heaters206 and amount of heat removed by the cooling apparatus 302.

For maximum throughput and efficiency, the process of forming glassarticles using the system of FIG. 1 involves cycling multiple moldsthrough the system. For any given product, there will be an ideal shapefor the glass articles to be formed. Some deviation from the ideal shapemay be tolerated. For cover glass applications, the acceptable deviationwill typically be very small, e.g., within ±50 microns. Each mold can bedesigned to yield a glass article that has the ideal shape within theacceptable deviation. If all the molds cycled through the system are sodesigned and have the same heat transfer properties, then the glassarticles they produce should have consistent shapes that match the idealshape within the acceptable deviation. However, the molds will typicallynot have the same heat transfer properties due to variations in moldmaterials, coatings, or processing. These variations may come from themolds experiencing different number of cycles or from the molds beingrefurbished. The differences in heat transfer properties of the moldsmay appear, for example, as differences in mold surface emissivities ordifferences in interface conduction between the mold and glass.

The shape of a glass article is affected by thermal gradients in theglass when the glass is conformed to the mold. The thermal gradients inthe glass are affected by the temperature of the mold, and thetemperature of the mold is affected by the heat transfer properties ofthe mold. In one aspect of the present invention, mold temperature iscontrolled to compensate for differences in heat transfer properties ofthe molds so that the glass articles produced by the molds haveconsistent shapes. A heat exchanger placed below the mold is used toactively control mold temperature. The heat transfer between the heatexchanger and mold may be by conduction, convection, or radiation. Inone embodiment, the heat exchanger is operated at an intermediate levelto remove a predetermined amount of heat from the mold. Additional orless heat can be removed by adjusting the heat exchanger above or belowthe intermediate level. The general procedure for forming glass articlesis to first establish a base process that produces glass articles withthe desired shape. Then, deviations of the glass articles from the idealshape are measured. The deviations are used to determine how much heatto remove from the molds during subsequent runs of the process.

FIG. 4A shows a cooling plate (or heat exchanger) 400 that can be usedto remove heat from a mold. In general, heat flux can be applied to thetop surface of the cooling plate 400 by means of radiation, convection,or conduction. The cooling plate 400 will then act to remove that heatby dumping the heat to fluid circulating through its passages. Althoughthe cooling plate 400 will be described in the context of cooling amold, it is noted that the cooling plate 400 can be employed in othercooling applications, such as cooling of electronics such as computerchips.

In one embodiment, the cooling plate 400 includes a top plate 402, amiddle plate 404, and a bottom plate 406. The middle plate 404 containsthe internal flow passages of the cooling plate 400. As shown in FIG.4B, the middle plate 404 has an outer band (or outer raised area) 408 inthe form of an encircling (or continuous) loop and an inner band (orinner raised area) 410 in the form of an encircling (or continuous)loop, with the outer band 408 circumscribing the inner band 410. Theinner band 410 has straight band sections 412, 414, which are generallyparallel to each other. The inner band 410 also has convoluted bandsections 416, 418 connecting the straight band sections 412, 414. Theconvoluted band sections 416, 418 are made of U-shaped loops.

An inflow channel 420 is defined between the outer band 408 and theinner band 410, and an outflow channel 422 is defined within the innerband 410. Inflow spacers 424 are arranged in the inflow channel 420within the U-shaped loops of the convoluted band sections 416, 418.Inflow spacers 425 are also arranged in the inflow channel 420 along themedian of the middle plate 404. Outflow spacers 426 are arranged in theoutflow channel 422 along the straight band sections 412, 414 or betweenthe straight band sections 412, 414 and the convoluted band sections416, 418. The outflow spacers 426 act as baffles to direct the path ofthe flow in the outflow channel 422.

The outer band 408 and spacers 424, 425, 426 are of the same height,whereas the inner band 410 is shorter than the outer band 408. When thetop plate 402 is stacked on the middle plate 404 (as shown in FIG. 4A),the outer band 408 and spacers 424, 425, 426 contact and seal againstthe top plate 402. Simultaneously, a gap 427 (in FIG. 4C) is createdbetween the top plate 402 and the middle plate 404 at locationscorresponding to the inflow channel 420, outflow channel 422, and innerband 410. The spacers 424, 425, 426 maintain a fixed distance betweenthe top plate 402 and the inner band 410, allowing the gap 427 to have aconsistent height across the cooling plate 400. As shown in FIG. 4C,fluid can flow through the gap 427, crossing from the inflow channel420, over the inner band 410, into the outflow channel 422. The inflowchannel 420 has to be flooded to allow the fluid to cross over from theinflow channel 420 into the outflow channel 422. In this case, the innerband 410 serves as a restriction between the channels 420, 422. Theresistance of the fluid flowing across gap 427 must be much greater thanthe resistance for the fluid to flow throughout the channel 420 or theresistance for the fluid to flow throughout the channel 422. Resistanceis defined in engineering as the pressure drop a fluid experiences as ittravels along a path divided by the flow rate of that fluid flowingalong that path. If the resistance of fluid crossing the gap 427 is Rg,the resistance of fluid to flow along the length of the inflow channel420 is Rs, and the resistance of fluid to flow along the length of theoutflow channel 422 is Rd. Then, each of Rd and Rs should be much lessthan Rg, e.g., at least 10 times less. This will ensure a very uniformflow of fluid cross all regions of the gap 427. Uniform flow is requiredin order to produce uniform cooling and a uniform temperature of thecooling plate 400. It is also important to note that the pressure of thefluid in the inflow channel 420 is largely uniform. The majority of thepressure change in the fluid occurs as the fluid cross the gap 427.

FIG. 4D shows a network of supply channels (or flow distributionchannel) 430 formed in the back of the middle plate 404. The network 430includes a main supply channel 432, running generally along the medianof the middle plate 404, and lateral supply channels 434 branching offthe main supply channel 432. An island 436 is formed in the main supplychannel 432. Fluid can move along the main supply channel 432 and aroundthe island 436 to reach the lateral supply channels 434. A dischargehole 437 extends from the island 436 to the outflow channel 422 (in FIG.4B). Main supply holes 438, 439 and crossover holes 440 are providedgenerally along the median of the main supply channel 432. The supplyholes 438, 439, 440 extend from the back of the middle plate 404 to theinflow channel 420 (in FIG. 4B). Auxiliary supply holes 442 are providedalong the periphery of the middle plate 404. The auxiliary supply holes442 are located at the ends of the lateral supply channels 434 andextend from the back of the middle plate 404 to the inflow channel 420.The network 430 enables quick distribution of fluid to the inflowchannel 420. As soon as fluid is delivered to the main supply holes 438,439, the fluid will spread through the network 430 to the crossoverholes 440 and peripheral supply holes 442 and then enter the inflowchannel 420.

The bottom plate 406 has supply holes 444, 445 (in FIG. 4E) anddischarge hole 437 (in FIG. 4E). When the middle plate 404 is stacked onthe bottom plate 406, the supply holes 444, 445 of the bottom plate 406will be aligned with the main supply holes 438, 439 of the middle plate406, and the discharge hole 437 of the bottom plate 406 will be alignedwith the discharge hole 437 of the middle plate 404. In use, supplyfluid tubes 446, 447 (in FIG. 4A) are coupled to the supply holes 444,445 of the bottom plate 406, respectively, and a discharge fluid tube448 (in FIG. 4A) is coupled to the discharge hole 437 of the bottomplate 406. Cooling fluid in the supply fluid tubes 446. 447 is deliveredto the main supply holes 438, 439 and then distributed to the inflowchannel 420 via the network 430. Preferably, the cooling fluid is gas,such as air. The fluid in the inflow channel 420 when at a sufficientlevel will cross over into the outflow channel 422 at several(infinitely many) points along the inner band 410. Fluid is dischargedfrom the outflow channel 422 through the discharge hole 437 in themiddle plate 404 and the discharge hole 437 in the bottom plate 406 intothe discharge fluid tube 448.

The passages in the cooling plate have been designed such that the fluidwill absorb as little heat as possible while in the inflow channel 420.If the fluid heats up as it travels along inflow channel 420, then itwill result in a nonuniform temperature of cooling plate 400. It ispreferred that the fluid heats up as it passes over the gap 427 (in FIG.4C), where the flow is uniformly distributed. If fluid heats up as itpasses over the gap 427, it will result in an overall uniformtemperature of the cooling plate 400. The inflow channel 420 and gap 427are sized such that most of the heat that the fluid absorbs occurs asthe fluid passes over the gap 427. For example, the inflow channel 420is larger than the gap 427 so that the inflow channel 420 has a lowerconvective heat transfer coefficient than the gap 427.

The middle plate 404 enables parallel distribution of fluid across thecooling plate 400. This parallel distribution has the net effect ofminimizing temperature gradients across the cooling plate 400, whichwill allow the cooling plate 400 to provide uniform cooling to the mold.The network 430 and crossover holes 440 is designed to get the fluid tospread out to the inflow channel 420 with as little resistance aspossible and with a temperature that is as close to the temperature ofthe inlet fluid, i.e., the temperature of the fluid supplied to thesupply tube 446, as possible. If the middle plate 404 did not includethe network 430 and the crossover holes 440, fluid would come into themain supply holes 438, 439 and into the inflow channel 420. The fluidwould then spread out in the inflow channel 420. However, as the fluidis moving through the inflow channel 420, it will absorb heat from thewalls of the middle plate 404. However, for uniform cooling and uniformtemperature of the cooling plate 400, it is desirable to minimize theheat the fluid absorbs as it spreads through the inflow channel 420. Byincluding the network 430 and the crossover holes 440, the relativelycold fluid can move more directly to the areas where it is needed, i.e.,the entire periphery of the entrance to the gap 427, before it has achance to heat up.

The plates of the cooling plate 400 are made of a material that has highthermal conductivity and good oxidation resistance and stability, i.e.,does not break down or shed, at high temperature. Using a material withhigh conductivity promotes thermal uniformity of the cooling plate 400.In one example, the plates are made of nickel. In another example, theplates are made of copper, which is then coated with an oxidationresisting coating such as nickel or gold. The plates could also be madeof a high temperature bronze material.

The plates of the cooling plate 400 can be assembled together using anysuitable means. In one example, braze material such as a silver-basedmetal is used to assemble the plates together. The silver-based metalhas a melting point higher than the maximum operating temperature of theplate assembly. The braze material is applied to the outer band 408 andspacers 424, 425, 426. The braze material forms a seal between the topplate 402 and the middle plate 404 at the locations of the outer band408 and spacers 424, 425, and 426. The bond provided by the brazematerial allows the gap 427 to remain at a uniform distance all aroundthe inner band 410, even when the inflow and outflow channels 420, 422are filled with pressurized fluid. The fluid must necessarily bepressurized in the inflow channel 420 in order to force the fluid acrossthe gap 427. The fluid is also at a pressure slightly above atmosphericpressure in the outflow channel 422 because there is a small pressuredrop as the fluid flows through the outflow channel 422 and out of thedischarge fluid tube 448.

FIG. 5A shows a mold support system 500 that allows the cooling plate400 to be placed below a mold while supporting the mold. The moldsupport system 500 can be be arranged at any station as shown at 500 inFIG. 3. The mold support system 500 includes a primary base 502 mountedon primary base standoffs 504 projecting upwardly from the indexingtable 104. The primary base standoffs 504 are secured to the primarybase 502 and indexing table 104 using any suitable means. A mold carrier506 is supported above the primary base 502 by standoff tubes 508. Thestandoff tubes 508 are coupled to the primary base 502 via a standoffbase 510 and to the mold carrier 506 via a standoff mounting block 512.The standoff tubes 508 are thin-walled to minimize conduction alongtheir walls. The mold carrier 506 includes a base plate 516 and a plenum518. An adapter plate 514 is attached at its bottom to the standoffmounting block 512 and at its top to the base plate 516. The plenum 518is mounted on the base plate 516. The base plate 516 may have featuressuch as pins on its top surface that engage features such as holes inthe bottom surface of the plenum 518.

The mold 214 is mounted on the top surface of the plenum 518. In oneembodiment, mold alignment tabs 520 are provided at the side of theplenum 518 to assist in aligning the mold 214 with the top surface ofthe plenum 518. In this embodiment, the mold 214 simply rests on theplenum 518, with only its weight holding it onto the plenum 518. Adifferent method of aligning the mold 214 with the top surface of theplenum 518 may be used, such as locating pins on the top surface of theplenum 518 that engage holes in the bottom surface of the mold 214.

In another embodiment, mold carrier 506, i.e., the base plate 516 andplenum 518, and the mold 214 are bolted together. Then, vacuum is usedto clamp the mold carrier 506 down to the adapter plate 514. FIG. 5Bshows the adapter plate 514 with a vacuum groove 511 and vacuum holes513. The vacuum holes 513 are connected to a vacuum hold-down tube 515.Vacuum can be applied to the vacuum holes 513 and then the vacuum groove511 via the vacuum hold-down tube 515. Vacuum in the vacuum groove 511will clamp the base plate 516 to the adapter plate 514. The vacuum holes513 in the adapter plate 514 may be connected to similar holes in thebase plate 516 and plenum 518 so that vacuum can be applied to theunderside of the mold 214 in order to clamp the mold 214 down to themold carrier 506.

Returning to FIG. 5A, the plenum 518 provides a chamber 522, which islocated between the bottom surface of the mold 214 and the top surfaceof the base plate 516. A service tube 523 passes through the indexingtable 104, primary base 502, adapter plate 514, and base plate 516. Theservice tube 523 is exposed at the top surface of the base plate 516 tothe chamber 522. The service tube 523 can be used to perform serviceswithin the chamber 522. For example, the service tube 523 can be used toprovide vacuum in the chamber 522. The vacuum provided in the chamber522 can be applied in between the mold 214 and the glass 525 on the mold214 via vacuum hole(s) in the mold 214. The service tube 523 can also beused to deliver a gas to the chamber 522. In this case, holes run fromthe bottom surface of the mold 214 to the top surface of the mold 214.The holes will be exposed to the chamber 522. By leaving a gap betweenthe cooling plate 400 and the bottom surface of the mold 214, the gasthat enters the chamber 522 is allowed to disperse and go through theholes in the mold 214. When the glass 525 is sitting on the top surfaceof the mold 214, the gas can be supplied to the interface between theglass 525 and mold 214 in order to lift the glass off the mold, e.g.,after the glass has been reformed.

The cooling plate 400 is located at the top of the chamber 522 and belowthe mold 214. Preferably, the cooling plate 400 is in close proximity,but not in physical, contact with the mold 214. This would allow heattransfer from the mold 214 to the cooling plate 400 to occur primarilyby radiation. For radiative heat transfer, there should be a path ofradiation between the cooling plate 400 and the mold 214. Separating thecooling plate 400 from the mold 214 allows the design of the mold 214 tobe independent of the design of the cooling plate 400, or vice versa.This would ultimately reduce the manufacturing cost of the mold.

Supply standoff tubes 446, 447 and discharge standoff tube 448 passthrough the indexing table 104, primary base 502, adapter plate 516, andbase plate 516 and are connected to the cooling plate 400. The tubes446, 447, 448 serve to pass cooling fluid to and from the cooling plate400. The tubes 446, 447, 448 are thin-walled tubes that have highresistance to heat conduction that occurs between the cooling plate 400and base plate 516. By having high heat conduction, the cooling plate400 is thermally isolated such that its temperature can be easilyadjusted by varying the flow rate of cooling fluid to it. The mold 214can also be thermally isolated to allow its temperature to be adequatelycontrolled by the cooling plate 400.

Typically, the temperature of the cooling plate 400 is maintained at anintermediate value by circulating fluid through the cooling plate 400 atan intermediate flow rate. The temperature of the cooling plate 400 canbe adjusted by increasing or decreasing the flow rate of the circulatingfluid from the intermediate flow rate. As the temperature of the coolingplate 400 is adjusted, the temperature of the mold 214 will be adjusted.For example, the temperature of the cooling plate 400 can be reduced byincreasing the flow rate of the circulating fluid, which would lead toan increase in radiative heat transfer from the mold 214 to the coolingplate 400 and a corresponding decrease in the temperature of the mold214. Conversely, the temperature of the cooling plate 400 can beincreased by decreasing the flow rate of the cooling fluid circulatedthrough the cooling plate 400, which would lead to a decrease inradiative heat transfer from the mold 214 to the cooling plate 400 and acorresponding increase in the temperature of the mold 214. Heat removalfrom the mold 214 will be relatively uniform due to the design of theinternal passages of the cooling plate 400 that minimize temperaturegradients across the cooling plate 400. The cooling plate 400 allows thecooling fluid to remove heat as effectively as possible such that aknown mass of cooling fluid produces a deterministic and repeatableamount of cooling.

Metrology is an important aspect of determining deviation in shapes ofglass articles in order to better control the process of making theglass articles. In one aspect of the invention, a metrology system isprovided that measures quickly and accurately a discrete set of pointson a glass article. In one embodiment, as shown in FIG. 6A, themetrology system 601 includes a mounting block 600 having a flat topsurface, or measurement surface, 602. Supports 604 are attached to themeasurement surface 602 and are provided to support a glass article tobe measured, such as glass article 606. In one embodiment, at leastthree supports 604 are attached to the measurement surface 602 toprovide at least three contact points for the glass article 606. Thesupports 604 are arranged to form a stable structure for supporting theglass article in a plane parallel to the measurement surface 602. Forexample, in FIG. 6, the three supports 604 are arranged in a trianglethat is large enough to stably support the glass article. The supports604 may be truncated cone supports, with the truncated end set to aminimum required to provide a stable structure and minimize the contactarea between the supports 604 and the glass article 606.

Alignment guides 608 are attached to the measurement surface 602 atlocations outside of the support structure formed by the supports 604.In one embodiment, the alignment guides 608 are arranged to form acorner that will engage a corner of a glass article 606 placed on thesupports 604. The alignment guides 608 thus serve as a reference datumfor placing a glass article on the supports 604 so that measurements canbe made consistently using the system. The alignment guides 608 engagethe glass article 606 via tabs 609, which are pointed or truncated orotherwise shaped to minimize the contact area between the alignmentguides 608 and the glass article 606. The mounting block 600 sits on topof legs 611. Preferably, legs 611 can be adjusted such that the mountingblock 600 is tilted at two angles such that the glass article 606 tendsto slide with the aid of gravity into slight contact with tabs 609. Theangles are typically less than 5 degrees.

Below the bottom surface of the mounting block are laser gauges 610. Thelaser gauges 610 are secured to the mounting block 600 via clampingrings 612. The clamping rings 612 grip the laser gauges 610 like acollet when a screw is tightened. The clamping rings 612 allow the lasergauges 610 to be moved slightly along their axes prior to tightening.The clamping rings 612 also keep the laser gauges 610 rigidly connectedto the mounting block 600 after they have been tightened such that thereis no looseness that would cause error in reading the position of theglass. As shown in FIG. 6B, the laser gauges 610 are inserted in holes614 in the mounting block 600. Laser air purge fittings 616 mounted onthe sides of the mounting block 600 are in communication with the holes614 through cross-drilled holes in the mounting block 600. The laser airpurge fittings are used to supply clean gas flow, such as air flow, tothe holes 614 in order to purge from the holes 614 any particles thatmay have fallen into the holes 614 and onto the top of the laser gauges610.

The mounting of the laser gauges 610 may be such that their measurementdirections are perpendicular or inclined to the measurement surface 602and intersect discrete points on the glass article 606. At least onelaser gauge 610 is needed to make measurements at a discrete point onthe glass article 606. Where multiple laser gauges 610 are used, eachlaser gauge 610 would be responsible for one discrete point on the glassarticle 606. The laser gauges 610 operate by launching laser light atthe glass article 606 and detecting the reflected light from the glassarticle 606. The measurements made by the laser gauges 610 are recordedin a suitable medium, such as an electronic data storage, and processedby a computer. A program on the computer takes the measurements made bythe laser gauges 610 and computes the distances between the discretepoints on the glass article 606 and the laser gauges 610, or anotherreference datum, along the measurement directions of the laser gauges610. The measured distances are compared to target distances, whichwould have been determined for an ideal glass shape either using thesame metrology system or by computer modeling. Any deviations in themeasured distances from the target distances are stored in a suitablemedium, such as an electronic data storage, and later used to improvethe process, e.g., to control mold cooling or removal of heat from theradiation emitter body.

In FIG. 6B, an axial hole 620 is drilled through each of the supports604. Vacuum pressure is transmitted to the axial holes 620 using vacuumfittings 622 and cross-drilled holes (not shown) in the mounting block600. The vacuum pressure is used to clamp the glass article 606 to thesupports 604 while measurement is being taken. Before the glass article606 is clamped to the supports 604 by vacuum pressure, a slight positiveair pressure can be pushed through the axial holes 620 to lift the glassarticle off the supports 604. This would eliminate all friction betweenthe glass article 606 and the supports 604 and allow the glass article606 to positively rest against the tabs 609 of the alignment guides 608.Then, the vacuum pressure can be subsequently applied to clamp the glassarticle 606 to the supports 604. If the glass article 609 is not floatedagainst the tabs 609, an operator would have to be relied on topositively locate the glass article 606 against the tabs 609. Usingpositive air pressure to float the glass article 606 into place can helpeliminate operator error.

FIG. 6C shows another metrology system that measures points on a glassarticle. The metrology system includes a displacement gauge 630 mountedto a fixture 632. The fixture 632 has a mounting block 634, whichprovides a measurement surface 636 (similar to measurement surface 602in FIG. 6A). The displacement gauge 630 is mounted below a window 638 inthe mounting block 634 and makes measurements through the window 638.Supports 640 (similar to supports 604 in FIG. 6A) and alignment guides642 (similar to alignment guides 608 in FIG. 6A) are arranged on themeasurement surface 636 for placement of a glass article 644 relative tothe measurement surface 636. The alignment guides 642 or glass article644 may be arranged such that the portion of the glass article 644 to bemeasured is approximately centered with the window 638.

Preferably, the displacement gauge 630 uses a non-contact displacementsensor to make measurements. A non-contact displacement sensor ispreferred for the metrology system because it will not involve physicalcontact with the glass article that may deform the glass article as themeasurement is taken. Several different types of non-contactdisplacement sensors may be used. A laser triangulation sensor is oneexample and operates by measuring the position where a laser linecontacts or reflects off a surface. Clear or highly reflective materialslike glass are configured to reflect the laser directly back into thesensor (specular reflection). Non-specular materials are configured withthe laser orthogonal to the surface, and the sensor detects the diffusereflection from the surface. Examples of laser triangulation sensors areavailable as LK series sensors from Keyence and optoNCDE series sensorsfrom Micro-Epsilon.

Another example of a non-contact displacement sensor is a spectralinterference laser displacement sensor, which operates by measuring theinterference of broad wavelength light reflected off a reference surfaceand target surface. The spectral content of the returned signal isspread spatially using a diffraction grating and the resulting signal isimaged on a CCD. The interference pattern is analyzed to extractdisplacement data. Depending on the distance from the reference totarget, the various spectra will interfere either by adding thereference and target signals together or canceling the reference andtarget signals out or somewhere in between. Examples of spectralinterference laser displacement sensors are available as SI-F seriessensors from Keyence.

Another example of a non-contact displacement sensor is a confocalchromatic displacement sensor. In this sensor, two lenses (or curvedmirrors) are arranged confocally to one another with their focusesmatching. With the confocal chromatic measuring principle, white lightis split into different spectra by lenses and focused on an objectthrough a multi-lens optical system. The lenses (or curved mirrors) arearranged such that the light is broken down by controlled chromaticaberration into monochromatic wavelengths depending on the displacement.Examples of confocal chromatic displacement sensors are available asconfocal DT series sensor from Micro-Epsilon.

Although a non-contact displacement sensor is preferred for use in thedisplacement gauge 630, it is possible that a contact displacementsensor can also be used. The contact displacement sensor will preferablymake measurements with a very low force that would not distort thearticle being measured. A linear variable differential transformer(LVDT) position sensor is one example of a contact displacement sensorthat could be used.

In one embodiment, the displacement gauge 630 uses a laser triangulationsensor to make measurements. The measurement axis of the displacementgauge 630 is generally along line 646. The measurements are made byoperating the displacement gauge 630 to direct a laser light to a pointnear the center of the glass article 644. The light strikes the glassarticle 644 and is reflected back to the displacement gauge 630. Thesensor in the displacement gauge 630 detects the reflected light. Thesensor output is transmitted to a laser readout machine 648. Thedisplacement gauge 630 may communicate with the laser readout machine648 via a wired or wireless connection. The laser readout machine 648displays the displacement measurement from the sensor. The laser readoutmachine 648 may also store the measurement for later use or transmit themeasurement to another system.

The metrology system may be used to measure deviation of a glass shapefrom an ideal. In one example, the system is used to measure deviationof a flat section of a glass article from the ideal. For this example, aflat glass article with sub-micron flatness is initially placed on thefixture 632 and the laser displacement gauge 630 is zeroed. Instead ofzeroing the laser displacement gauge 630, the response of the laserdisplacement gauge 630 to the flat glass article may be simply recorded.Then, any successive glass article may be placed on the fixture 632, andthe displacement reading measured by the laser displacement gauge 630will correspond to the flatness of the glass article.

FIG. 6D shows a graph of repeatability test data collected using thesystem of FIG. 6C. For the data shown in the graph, a single piece ofglass article was repeatedly loaded onto the fixture 632 by hand, andmeasurements were recorded. The flatness value of the glass article wasfound by placing a reference glass article with flatness less than 1micron onto the fixture 632 and zeroing the laser displacement gauge630. The duration of the test was 30 minutes. If the laser gauge waszeroed only once at the start of the test period, then significant driftin the reading occurred over time, as shown by the line 650. However, ifthe reference glass article was placed back on the fixture 632 and thelaser gauge was re-zeroed before every reading during the test period,then the repeatability of the measurement was within 0.7 micron, asshown by the line 652.

In another example, the metrology system is used to measure deviation ofa curved section of a glass article from the ideal. In this case, areference 3D shape is placed on the fixture 632 and the response of thelaser displacement gauge 630 to the reference 3D shape is recorded. Thedisplacement reading measured by the laser displacement gauge 630 forany subsequent 3D shapes can be compared to the displacement reading forthe reference 3D shape.

FIG. 6E shows another metrology system that measures the displacement ofpoints on a glass article 670. The glass article 670 is supported on aglass support fixture 672. Above the glass support fixture 672 is aprobe support fixture 674. Displacement gauges 676, which may employ anyof the sensors described above, are supported in and along the probesupport fixture 674. The displacement gauges are in opposing relation tothe glass article 670. Each displacement gauge 676 will be responsiblefor measuring a distance between a point on the glass article 670 andthe displacement gauge 676, i.e., displacement of a point on the glassarticle 670. Signals from the displacement gauges 676 can be collectedby a measurement module 678, which may process the signals to determinethe shape of the glass article 670, e.g., using a processor. Themeasurement module 678 may output the measured shape to a system forcontrolling the shape of a glass article. The measurement module 678 mayadditionally compare the measured shape to a reference shape and outputinformation about deviation of the measured shape from the referenceshape to the system for controlling the shape of a glass article. Such asystem will be described in more detail below.

Returning to FIG. 1, cycle time may be improved by preheating the mold108 before a 2D glass sheet is placed on the mold 108 and the mold 108is indexed into any of the HT modules 110. In one aspect of theinvention, a heating system for preheating a mold is provided. In oneembodiment, in FIG. 7A, a heating module 700 for preheating a moldincludes a heater assembly 702, which includes an array of radiantheaters 704 that operate in the infrared range. The heater assembly 702is mounted within a cavity 706 of a shield box 708. The shield box 708largely blocks high intensity light and heat from emanating out of theheating module 700 to where the light and heat could be dangerous tohuman operators. The base 710 of the shield box 708 has a slot 712. Whenthe heating module 700 is mounted for use, as shown in FIG. 7B, the topof the indexing table 104 extends through and is translatable relativeto the slot 712.

Fences 714, made of refractory material, are provided on the top of theindexing table 104. The space between each adjacent pair of fences 714defines one of the stations 106. When a station 106 is indexed with theheating module 700, the fences 714 adjacent the station 106 close theopen sides of the slot 712 of the shield box 708. A chamber 716 is thendefined between the fences 714, the heater assembly 702, and theindexing table 104. Mold 214 to be heated by the heater assembly 702 isinserted into the chamber 716 via the mold support system describedabove. In this position, the heater assembly 702 can be operated todeliver very intense heat flux that can boost the temperature of themold 214 quickly during a single index dwell of the system. In oneembodiment, the bulk temperature of the mold is boosted by at least 40°C. in a single index dwell. Typically, the bulk temperature of the moldis boosted by up to 100° C. in a single index dwell. An index dwell is atime period in which the indexing table is stationary and stations areindexed with HT modules. The advantage of preheating the mold is thatthe time required to heat the mold to forming temperature when the glassis in placed on the mold and indexed into the HT modules would bereduced, which would reduce cycle time.

FIG. 7C shows an electrical connector 726 at the top of the heatingmodule 700. The electrical connector 726 is coupled to the heaterassembly 702 and may be connected to the cable 728 to allow delivery ofelectrical power to the heater assembly 702. FIG. 7C also shows acooling unit 718 mounted above the heater assembly 702. The cooling unit718 can be operated to maintain the heater assembly 702 at a safetemperature. The cooling unit 718 may include a chamber 720 throughwhich cooling fluid is circulated, with appropriate fittings 722, 724(also see FIG. 7B) for supplying fluid to and withdrawing fluid from thechamber 720. The cooling fluid is preferably water, although air orother cooling fluid, gas or liquid, may be used.

The infrared heater assembly 702 may be replaced with an inductionheater. The induction heater can be made of one or more electrodes thatcan be energized to generate a high-frequency electromagnetic (EM)field. The EM field would create eddy electrical currents in the moldthat will resistively heat the mold. The inductive approach can enablethe temperature of the mold 214 to be raised even faster than theinfrared heating approach. For uniform heating of the mold, theelectrode(s) should be shaped or positioned above the mold 214 such thatthere is a substantially uniform gap between the electrode(s) and themold surface.

The 2D glass sheets that can be formed into 3D glass articles willdepend in part of the desired attributes of the 3D glass articles. For3D glass cover applications, high strength and resistance to damage areimportant. Typically, the requirements of these applications can be metby ion-exchangeable glasses. Ion-exchangeable glasses are characterizedby the presence of small alkali metal or alkaline-earth metal ions thatcan be exchanged for larger alkali or alkaline-earth metal ions duringan ion-exchange process. Typically, ion-exchangeable glasses arealkali-aluminosilicate glasses or alkali-aluminoborosilicate glasses.Specific examples of ion-exchangeable glasses are disclosed in U.S. Pat.Nos. 7,666,511 (Ellison et al; 20 Nov. 2008), 4,483,700 (Forker, Jr. etal.; 20 Nov. 1984), and U.S. Pat. No. 5,674,790 (Araujo; 7 Oct. 1997);U.S. patent application Ser. Nos. 12/277,573 (Dejneka et al.; 25 Nov.2008), 12/392,577 (Gomez et al.; 25 Feb. 2009), 12/856,840 (Dejneka etal.; 10 Aug. 2010), 12/858,490 (Barefoot et al.; 18 Aug. 18, 2010), and13/305,271 (Bookbinder et al.; 28 Nov. 2010); and U.S. ProvisionalPatent Application No. 61/503,734 (Dejneka et al.; 1 Jul. 2011).

The general procedure for making glass articles includes supporting amold at a station and indexing the station with the heating module 700(in FIGS. 7A-7C) so that the mold can be preheated. Within the same timeframe, 2D glass sheets are preheated at the loading area 118 (in FIG.1). After the mold is preheated, a preheated 2D glass sheet is loadedonto the mold and the mold and 2D glass sheet are translated into afirst sequence of HT modules 110 (in FIG. 1). These HT modules 110 willbe operating in the heating mode so that the 2D glass sheet can beheated to a temperature at which it is soft enough to be conformed tothe mold surface to form a 3D glass article, typically a temperaturebetween the annealing point and softening point of the glass. Force maybe used to conform the 2D glass sheet to the mold surface. The mold and3D glass article are then translated through a second sequence of HTmodules 110 operating in the cooling mode so that the 3D glass articlecan be cooled down to a temperature at which it can be handled,typically to a temperature below the strain point of the glass. From thesecond sequence of HT modules operating in the cooling mode, the moldand 3D glass article are translated to the unloading section of thesystem, where the 3D glass article is unloaded from the mold. The moldis then cycled again through the system. For continuous production ofglass articles, molds are placed on stations of the system until all thestations are filled with molds. Each mold will experience the same cycledescribed above until it emerges in the unloading section with a 3Dglass article.

The 3D glass articles and molds are tracked so that the mold thatproduces each 3D glass article is known. The shape of each 3D glassarticle is then measured, e.g., using the metrology system describedabove and in FIG. 6. The deviation of the shape of the 3D glass articlefrom an ideal shape is determined. If the deviation is not withinacceptable limits, measures are taken to improve the shape. Measures maybe taken to improve the shape even if the deviation is within acceptablelimits, i.e., in order to get as close to the perfect shape aspractical. One measure that could be taken is active control of thetemperature of the mold that is producing the deviant 3D glass article.Typically, the best approach is to control the temperature of the moldat the time when the force that is used to hold the 3D glass articleagainst the mold is released. This occurs after the glass has beenconformed to the mold. It is assumed that if the glass has conformed tothe mold and has not bonded to the mold, then the remaining mechanism bywhich the glass can warp, and hence lose shape, are thermal gradients inthe glass when holding force is released. The thermal gradients in theglass can be controlled through the temperature of the mold. Thedeviation of the shape of the 3D glass article produced by the moldpreviously will provide the clue as to how much cooling of the moldwould be needed in order to subsequently produce a 3D glass article withthe correct shape. The amount of heat to remove from the mold will varyfrom one mold to the next due to variations in heat transfer propertiesof the mold, as already discussed above. Therefore, it will be importantto measure the 3D glass article produced by each of the molds beingcycled through the system in order to determine how to adjust thetemperature of each of the molds. FIG. 8 is a graph showing how theshape of the 3D glass article responds to adjustment of mold coolingflow over several cycles. Line 800 represents the cooling plate flow.Lines 802, 804, 806 represent different points on the glass. As thecooling plate flow is adjusted to change the mold temperature, the shapeof the glass approaches the ideal, i.e., where deviation is nearly zero.

FIG. 9A shows a system 900 for controlling the final shape of a 3D glassarticle. In control system 900, the ideal shape of the 3D glass article902 and the measured shape of the 3D glass article 904 are received at asumming point 906. The ideal and measured shapes provided to the summingpoint can each be cast in terms of a set of shape metrics. FIGS. 10A and10B show examples of shape metrics that could be measured and used tocharacterize the shape of the 3D glass article. In FIG. 10A, shapemetric R1 represents the radius of curvature of a bend formed in a bendsection 1000 of the 3D glass article 1002. In FIG. 10B, shape metrics R2and R3 represent the radii of curvatures in a flat section 1004 of the3D glass article 1002. A combination of R2 and R3 may be another metric.The shape metrics shown in FIGS. 10A and 10B can be manipulated usingprocess parameters. One such process parameter is the mold temperature.The shape characteristics measured and provided to the summing point maybe based on one or more of the shape metrics described above or on adifferent set of shape metrics. The shape measurements may be obtainedfrom any of the metrology systems described above or from a differentmetrology system not described above.

The difference 907 between the ideal shape 902 and measured shape 904 isfed to a model-based control 908 containing a model 910 that correlatesglass shape to cooling flow rate. The output 912 of the model 910 is atarget cooling flow rate. The target cooling flow rate 912 and theactual cooling flow rate 914 are received at a summing point 916. Thedifference 917 between the target cooling flow rate 912 and actualcooling flow rate 914 is fed to a flow controller 918, whose output 920is provided to the system 930. The flow controller 918 could be anoff-the-shelf product or a proportional-integral based control scheme.The system 930 includes an associated set of cooling plate and mold(400, 214 in FIG. 5A). The cooling plate adjusts the temperature of themold using the mechanism already described above. Also, the moldtemperature is measured and used to update the model 910, as shown bythe arrow 932. The mold temperature may be measured using a pyrometerinstalled at the exit of the process. The measured mold temperature willaccount for any emissivity changes of the mold. The feedback 904 showsthat the shape of the 3D glass article that is formed by the mold of thesystem 930 is measured and returned to the summing point 906.

FIG. 9B shows another system 950 for controlling the final shape of a 3Dglass article. The control system 950 of FIG. 9B is similar to thecontrol system 900 of FIG. 9A, with the exception that the model-basedcontrol 952 contains two models 954, 956. In FIG. 9A, the model-basedcontrol 908 had only model 910. In FIG. 9B, model 954 correlates glassshape to mold temperature, and model 956 correlates mold temperature tocooling flow rate. In this case, the difference 907 between the idealshape 902 and measured shape 904 are fed to the model 954. The output958 of the model 954 is then fed to the model 956. The output 960 ofmodel 956 is the target cooling flow rate and is received at the summingpoint 916 along with the actual cooling flow rate 914. The remainder ofthe process continues as described above, except that only the model 954is updated with information about the mold temperature, as indicated byarrow 962. The control system 950 can be used when it is difficult todetermine a direct relationship between shape and cooling flow rate.

The models can be developed using experimental data. For example, FIG.11A shows change in mold temperature for a change in cooling flow ratefrom a maximum to a minimum. FIG. 11B shows change in mold temperaturefor a change in cooling flow rate from a minimum to a maximum. In FIGS.11A and 11B, the stars 1100 represent the mold temperature, and thecircles 1102 represent the cooling flow rate. The cooling fluid for thedata shown in FIGS. 11A and 11B is air. From the data shown in FIGS. 11Aand 11B, a cooling flow rate to mold temperature model can bedetermined. An inverse of this model will yield a mold temperature tocooling flow rate model. One of the ways the model could be formulatedas a first-order-plus-dead-time (FOPDT) model. However, care should betaken to determine the model parameters over a narrow operating rangeprimarily due to the high nonlinearity of the process. The derivationbelow is an example of how such a model could be developed.

Any FOPDT model can be formulated as:

$\begin{matrix}{{Y(s)} = {\frac{K\;{\mathbb{e}}^{{- T_{d}}s}}{\left( {1 + {sT}} \right)}{U(s)}}} & (1)\end{matrix}$where Y(s) is the Laplace transformation of the output (moldtemperature), U(s) is the Laplace transformation of the input (coolingflow rate), K is the process gain (defined as the ratio of the change inthe output to the change in the input), T_(d) is the dead time (definedas the time it takes for the process to respond to an input change) andT is the process time constant (defined as time it takes for the processto go from the current state to 63% of the next steady-state).

Based on the data shown in FIGS. 11A and 11B, the model parametersobtained are −0.75 for the process gain (negative sign increase incooling flow rate decreases mold temperature), less than 1 cycle timefor the dead time, i.e., approximately 7 minutes, and 1 cycle time forthe process constant, i.e., approximately 7 minutes. Hence the coolingfluid rate (Q_(c)) to mold temperature (T_(m)) model is defined as:

$\begin{matrix}{T_{m} = {\left\lbrack \frac{{- 0.75}\;{\mathbb{e}}^{{- 7}\; s}}{\left( {1 + {7\; s}} \right)} \right\rbrack Q_{c}}} & (2)\end{matrix}$

The other models 910, 954 can be determined using an approach similar tothe one described above. However, as mentioned earlier, the modelparameters must be determined for a narrow operating region. Multiplemodel parameters can be generated for multiple operating regions andthen model parameters can be switched in real time depending on thecurrent operating region. The control systems 900, 950 may beimplemented on a computer or a programmable logic controller. Further,portions of the control systems 900, 950 may be implemented on acomputer. For example, the models 910, 954 may be implemented on acomputer.

When forming a 2D glass sheet into a 3D glass article, force is appliedto the glass in order to conform the glass to the mold. In a preferredembodiment, the forming force is produced by applying vacuum between themold and glass. The vacuum must be sufficient to force the softenedglass into full compliance with the mold surface. In general, this meansa vacuum level of over 20 kPa (or 3.5 Psi). After forming is complete,vacuum is maintained to hold the glass in compliance with the mold whileforming stresses relax and glass temperature equilibrates. For highstrength glasses, the high level of sodium in the glass can react atforming temperatures with the mold surface, creating corrosion anddeterioration of the mold surface. This reaction can be intensified byhigh contact pressure between the hot glass and the mold surface,leading to accelerated deterioration of the mold surface. Since highforce is only needed to initially form the glass, the vacuum can bereduced to a level just sufficient to hold the glass against the moldsurface once initial forming is complete.

From the above, forming of the glass into a 3D shape involves applying aforming vacuum force to conform the glass to the mold surface and thenreducing the forming vacuum force to a holding vacuum force to hold theglass against the mold. Forming generally takes place in less than 20seconds, while the glass may be held under vacuum for another 40 or moreseconds for best warp performance. The reduced force between the hotglass and mold would reduce the reaction between the sodium in the glassand the mold surface. For example, the vacuum may be reduced from 27 kPato 9 kPa after 25 seconds and then held at 9 kPa for an additional 35seconds in a two-stage vacuum process. Reduction in vacuum after forminghas been shown to significantly increase the number of forming cyclesbefore mold renewal is necessary. Additional step downs in vacuum may beadded as needed to create the best balance between holding force andmold life. This principle of stepping down the force applied to theglass after conforming the glass to the mold surface may be used withother methods of applying force to the glass, such as the plungermethod.

A process of forming a 3D glass article that minimizes warp in the glasscan be explained with reference to FIG. 12. In this figure, thetemperature of the portion of the glass that will be flat is indicatedat 1200; the temperature of the portion of the glass that will be curvedis indicated at 1202; the temperature of the portion of the mold thatcorresponds to the flat portion of the glass is indicated at 1204. Thetemperature of the portion of the mold that corresponds to the curvedportion of the mold is similar to 904.

Between time T1 and T2, the glass is heated to a forming temperature ina radiative environment, which may be provided by one or more HT modulesoperating in a heating mode. Preferably, the forming temperature isbetween the annealing point and softening point of the glass. The moldis heated along with the glass since the glass is on the mold duringthis time.

At time T2, the glass is at the forming temperature. Between time T2 andT3, while the glass is in the radiative environment, force is used toconform the glass to the mold. The force is produced by applying vacuumbetween the glass and mold. The radiative source at this stage isgenerally much hotter than the mold temperature in order to maintain theglass as soft as possible during the forming operation. The moldtemperature is generally held at a temperature about 50° C. to 70° C.above the viscoelastic transition region of the glass. While in theradiative environment, the glass will remain at an intermediatetemperature between the radiative temperature and the mold temperatureand well above the elastic transition. This would allow the bendingstresses generated in the glass by forming to relax while the glassremains conformed to the mold. The key is for the majority of themechanical stresses due to forming to relax by maintaining the glasstemperature well above annealing point. Thermal gradients are notimportant at this time because the glass is soft and stresses due tothermal gradient will relax quickly.

Between time T3 and T4, the glass is held against the mold by force. Theholding force is produced by applying vacuum between the glass and mold.Typically, there should be continuity between applications of theforming and holding forces, although the holding force may be reducedcompared to the forming force. While continuing to hold vacuum inbetween the glass and mold, the glass temperature is then matched tothat of the mold temperature and made as uniform as possible by indexingthe glass and mold into a radiative environment that matches the moldtemperature. Ideally, the mold temperature would remain above theannealing point, e.g., by 30° C.-50° C., allowing further relaxation ofresidual glass bending stresses. At time T4, the mold temperature, glasstemperature, and radiative environment temperature are substantiallyequal and uniform throughout. Thermal gradients in the glass should benear to zero as possible.

Immediately after time T4, vacuum is released from between the glass andmold, even though the glass is still nominally viscoelastic. The onlyremaining force on the glass would be gravitational, i.e., the weight ofthe glass itself. This is less than 0.1% of the force applied to formthe glass. Given the low applied force and extremely high viscosity ofthe glass, any additional sag or physical relaxation will be extremelyslow, on the order of several minutes.

After the vacuum release, the glass is cooled to the purely elasticzone. This cooling should take place very rapidly, on the order of 2minutes or less, so that any warp due to thermal gradients generatedduring cooling will not have time to relax by sagging. When the glasscomes to a uniform room temperature, it will then return to the shapedetermined by the mold. Thermal gradients generated during this rapidcool are relatively unimportant as long as they do not generate stresseshigh enough for significant viscous relaxation in the time allotted.

While the invention has been described using a limited number ofembodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

The invention claimed is:
 1. A glass molding system, comprising: a) anindexing table; b) a plurality of enclosures arranged along the indexingtable, wherein at least one enclosure comprises: i) at least one radiantheater arranged in the at least one enclosure; and ii) a radiationemitter body arranged in the at least one enclosure; and c) a pluralityof stations defined on the indexing table such that each of the stationsis selectively indexable with any one of the enclosures, wherein atleast one station comprises: i) a radiation reflector surface configuredto be in opposing relation to the at least one radiant heater in theenclosure when the at least one station is indexed with the at least oneenclosure; ii) a mold support system attached to the indexing table andconfigured to travel with the indexing table, iii) a mold disposed onthe mold support system, and iv) a cooling plate mounted below the moldon the mold support system and comprising a fluid inlet and a fluidoutlet for circulating a cooling fluid through the cooling plate,wherein the cooling fluid is not in direct communication with the mold;and wherein the radiation emitter body is located between the at leastone radiant heater and the radiation reflector surface and has a firstsurface in opposing relation to the at least one radiant heater and asecond surface in opposing relation to the radiation reflector surfacewhen the at least one station is indexed with the at least oneenclosure.
 2. The glass molding system of claim 1, further comprising acooling apparatus disposed at least partially in the at least one of theenclosures and operable to remove heat from the radiation emitter body.3. The glass molding system of claim 1, further comprising a pluralityof molds and mold support systems, each mold support system configuredto support one of the molds at one of the stations.
 4. The glass moldingsystem of claim 3, wherein the radiation reflector surface has anopening for receiving any one of the molds such that the radiationreflector surface circumscribes the mold.
 5. The glass molding system ofclaim 4, wherein an area of the opening in the radiation reflectorsurface is less than an area of the second surface of the radiationemitter body.
 6. The glass molding system of claim 4, wherein thecooling plate comprises a plate member having a first flow channel inwhich the cooling plate receives fluid, a second flow channel from whichthe cooling plate discharges fluid, and a barrier between the first flowchannel and second flow channel that allows fluid to cross over from thefirst flow channel to the second flow channel at several points along anentire length of the second flow channel.
 7. The glass molding system ofclaim 4, further comprising a heating apparatus arranged along theindexing table for preheating any one of the molds while the mold is ata station that is not indexed with any one of the enclosures, theconfiguration of the heating apparatus and arrangement of the heatingapparatus relative to the indexing table being such that any one of thestations can be indexed with the heating apparatus.
 8. The glass moldingsystem of claim 7, wherein the heating apparatus is configured to boostthe temperature of any one of the molds by a predetermined amount in asingle dwell of the indexing table.
 9. The glass molding system of claim3, further comprising means for measuring a shape of a three-dimensional(3D) glass article produced by any one of the molds.
 10. The glassmolding system of claim 9, wherein the measuring means comprises ameasuring surface, support elements on the measuring surface forsupporting the 3D glass article in a plane substantially parallel to themeasuring surface, and at least one displacement gauge configured tomeasure a displacement of a point on the 3D glass article when the 3Dglass article is supported by the support elements.
 11. The glassmolding system of claim 3, further comprising means for loadingtwo-dimensional (2D) glass sheets onto the molds and means for unloadingthree-dimensional (3D) glass articles from the molds.
 12. The glassmolding system of claim 11, further comprising means for preheating the2D glass sheets outside of the enclosures.
 13. The glass molding systemof claim 1, wherein each of the enclosures is a thermal enclosureprovided by a housing having an insulated refractory wall.
 14. The glassmolding system of claim 1, wherein the radiation emitter body has anemissivity greater than 0.8 and the radiation reflector surface has anemissivity less than 0.4.
 15. The glass molding system of claim 1,wherein the indexing table is a rotary indexing table.